Printed circuit boards (PCBs) are generally mounted in frames, with a large number of PCBs mounted in each frame, with as high a density as possible, in order to save space. A typical PCB comprises a pattern of electrical interconnections on a flat rectangular sheet of insulating material (such as glass-fiber reinforced resin) and carries a number of components on one of its flat faces. The four edges of the PCB can be referred to as a front edge, a back (or rear) edge, a top edge, and a bottom edge. The PCB slides into guide channels in the frame, the PCBs lying normally in a vertical plane with the top edge in a top guide channel, the bottom edge in a bottom guide channel, and the rear edge carrying a set of connections which mate with a corresponding set of connections mounted to the frame. The front edge of the PCB may carry two devices (one usually near the top, and one usually near the bottom) to aid in inserting, removing or retaining the PCB relative to the frame.
An example of a prior art device for performing this function is disclosed in U.S. Pat. No. 4,233,646 entitled "Latching Lever for Printed Circuit Boards" which issued to E. C. Leung and I. R. Revah on Nov. 11, 1980. The disclosed latching lever includes a latching mechanism which comprises a hooked portion flexibly connected to the body portion of the latching lever, an actuating member solidly connected to the hooked portion for moving the hooked portion relative to the body portion, and a stop portion, solidly connected to the body portion for limiting the movement of the actuating member. A stud carried by the PCB is engaged by the hooked portion of the lever to enable the lever to latch. Moving the actuating member disengages the hooked portion from the stud, thereby unlatching the lever, and leaving the lever free to pivot about its pivot point.
Such latching levers are commonly used in combination with PCBs having various widths of faceplates with accommodation for the lever being provided by a cutout in the end of the faceplate.
One such prior art latching lever 10 is illustrated in FIG. 1 of the accompanying drawings wherein the latching lever 10 and a corresponding PCB faceplate 8 are depicted in combination at an upper front corner of a PCB. The faceplate 8 includes an extension 9 which defines a cutout being occupied by the latching lever 10. The latching lever 10 includes a body portion 11, actuation member 12, and an arm portion 13 which is bifurcated in order to straddle the PCB (not shown). Operation of the latching lever is well known but is briefly reviewed here. In the latched position shown, a hooked portion not visible is held by a stud in the PCB so that the arm portion engages a U-shaped channel or the like formation in a mating apparatus (not shown) and so secures the PCB in the mating apparatus. Movement of the actuation member releases the hooked portion whereafter movement of the latching lever aids in removal of the PCB from the mating apparatus. The necessity of the cutout requires that the end portion of the faceplate be projected beyond any mounting point beween the faceplate and the associated circuit board. Therefore the faceplate is typically fabricated from a robust material, or a material which is not likely to suffer damage if subjected to mishandling such as accidental droppage.
A faceplate of lighter, less costly and less robust material is useful in an arrangement wherein the latching lever is of the same width as the faceplate. Such a latching lever is of a structure similar to that depicted in the previously mentioned patent but is modified to occupy that area previously occupied by the end projection of the faceplate. However widening of the latching lever required a wider hinge area over which the latching and unlatching stresses are transmitted. The larger area presented undesirable resistance to operation of the lever. A reduction of thickness of the hinge web reduced the resistance to operation but rendered the hinge failure-prone in the area of the hooked portion due to stress concentration.
Another problem with the latching lever of the previously mentioned patent is that its operation can be confusing to an uninitiated person. The confusion can result when the latching lever is in an extreme open position in the case where the circuit board is being inserted into a mating apparatus. In this case a portion of the body of the latching lever can contact the mating apparatus in the extreme position thus complicating normal circuit board insertion. The uninitiated person in frustration may deal a substantial wack with the heel of their hand to the faceplate. Such treatment tends to be damaging particularly to the cost reduced less robust faceplate.